1. Field of the Invention
The present invention relates to a device which provides an automatic reference point (usually atmospheric pressure) for pressure transducer setups that convert biological pressure signals from various invasive monitoring devices into electrical signals which can then be processed, displayed in various forms using various methods, and(or) stored using various methods.
Current pressure transduction and monitoring systems in use require that the pressure monitoring transducer(s) be connected to the chamber of measurement (e.g. the heart's right atrium, the radial artery, the pulmonary artery, et. al.) via a sealed, ideally non-compliant conduit containing a continuous, uninterrupted line of fluid between the chamber and said monitoring transducer. The fluid is usually 0.9% NaCl in water containing a small amount of the anticoagulant heparin sodium to prevent clotting of the invasive monitoring line. This fluid-containing conduit transmits the pressure impulse from the chamber of measurement to the pressure transducer.
In order that the pressure transduction into the electrical signal not be influenced by the hydrostatic height of the fluid in the conduit, the transducer is usually mounted at the bedside in a fixed position so that it sits at roughly the same horizontal height as the chamber being measured (e.g. the right atrium of the heart). Once set up in this fashion, any artifact due to fluid column height is eliminated. By convention, the hydrostatic height of the right atrium of the heart is generally used as the point of reference for all types of invasive monitoring. Even peripheral arterial lines.
Often, a three-way stopcock is used to temporarily interrupt this fluid continuity and allow the small remaining fluid at the transducer to be exposed to air, hence atmospheric pressure. This maneuver, referred to as "zeroing the transducer," allows, the operator to set the monitoring device to zero during this exposure to air; thus allowing all further pressure measurements once the fluid continuity to body chamber of measurement has been reestablished, to be expressed in relation to atmospheric pressure. This zeroing maneuver is important in that it allows each monitoring channel to be set at zero to match the electrical signal produced by the corresponding pressure transducer when said transducer is exposed to air rather than exposed to the fluid conduit connecting it with the monitoring line transmitting pressure in a bodily chamber.
The present invention provides a method of constant transducer reference with the use of a separate reference transducer and reference chamber thus eliminating the need for precise mounting of monitoring transducers at the level of the chamber of measurement while also providing a constant atmospheric zero reference to the monitoring channels. Such an invention would eliminate the need to "zero the transducer," i.e., expose each transducer to air via a 3-way stopcock while setting each corresponding monitoring channel to zero; during monitor setup and during patient transfer to another monitoring location (e.g. intensive care unit to operating room and back again would require three such setups and monitor zeroing maneuvers).
2. Description of Prior Art
Pressure transducer systems currently in use in clinical and research medicine utilize a variety of methods to convey pressure impulses arising from invasive monitoring devices like indwelling arterial catheters, central venous catheters, pulmonary arterial catheters, and left heart catheters and convert or transduce them into proportional analog and(or) digital electrical signals which can then be processed and(or) displayed on monitoring screens, graph paper, and other information display and recording devices (e.g. U.S. Pat. No. 3,946,724).
Many recent devices disclosed utilize various methods of electrical signal processing (e.g. U.S. Pat. Nos. 4,899,760, 4,890,630, 4,530,3265, & 4,190,886) to provide a more reliable and accurate signal display and analysis. None of these prior art references address the issue of simplification of the process of levelling and zeroing the transducer by providing a more constant external reference.